In the field of data communication, it is often desirable to modify data being transmitted to or over a medium. For example, in code division multiple access (CDMA) communication systems, data to be transmitted and a chipping code are input into a modulator to modulate a carrier waveform using frequency modulation based on the input data and the chipping code. The resulting waveform is a frequency modulated sinusoid that is transmitted over the air interface. A demodulator demodulates the frequency modulated waveform using the chipping code and extracts the data signal.
One problem with techniques, such as CDMA, that directly modulate a carrier waveform is that the resulting signal is detectable and identifiable over the air interface as communications. Because the signal is detectable and identifiable as communications, it can be received and it is, therefore, vulnerable to a brute force attack whereby the chipping code can be discovered through brute force trial and error, and, once the chipping code is discovered, the transmitted data can be decoded.
In multiple access scenarios, it is desirable to use scrambling to reduce or avoid interference between signals of different users. To allow multiple access, signals have been conventionally multiplexed in (i) the frequency domain (FDMA—transmitting at different frequencies); (ii) time domain multiple access (TDMA—transmitting at different times); (iii) by using different codes (CDMA—using different chip codes); or (iv) using different spaces/mediums (using separate wires for each signal, or assigning a frequency for a given area, as is done in cellular systems); or (v) a combination of these. The main reason for this is that two or more signals using the same frequency transmitted at the same time in the same medium interfere with each other, and hence the information they carry is irrevocably destroyed. Code scrambling, as described herein, allows a totally new type of multiplexing scheme, which can work in conjunction with any of these (FDMA, CDMA, TDMA, or a combination thereof) or other existing schemes. This is because two or more signals using the same frequency can be scrambled with different codes, and thus even if they are transmitted at the same time in the same medium, these signals do not interfere such that the information they carry is irrevocably destroyed.
More generally, when data is stored on, transmitted to, or received from a medium, it may also be desirable to encode or scramble the data in an invertible manner for security and/or multiple access for later detection. Existing techniques based on direct carrier modulation are suboptimal for the reasons stated above with regard to CDMA communications systems.
Accordingly, there exists a need for improved methods, systems, and computer readable media for scrambled communication of data to, from, or over a medium.